There are various forms of screwcapping machines on the market today which are designed to screw closures onto a series of containers which are sequentially advanced through the machine. Three such screwcapping machines are taught in U.S. Pat. Nos. 3,242,632; 3,491,516; and 3,537,231. In turret-type machines, a plurality of screwcapping heads are arranged in a circular fashion and are selectively brought into alignment with a container which is to be capped. With these types of machines, one must consider the weight of the screwcapping heads in relation to their rotational speed. The reason for this is that the inertia of a heavier screwcapping head rotating about its own axis produces a certain torque which varies with the square of the speed. A light screwcapping head therefore encounters less inertia. This factor is important because a screwcapping machine is normally set for one preferred line speed at which the closures are torqued at a predetermined value onto the containers. Due to common line problems, it becomes necessary for the operator to vary the speed of the screwcapping machine to accommodate different size containers, different weight containers, containers having a different number of screw threads, etc. Such action affects the torque at which the closures are threaded onto the containers.
With the advent of screwcapping heads having magnetic clutches, such as is taught in U.S. Pat. Nos. 4,364,218 and 4,492,068 and in allowed U.S. Ser. No. 602,237, filed Apr. 19, 1984, and assigned to Aluminum Company of America, the weight of the screwcapping heads has increased significantly. Now the torque on the screwcapping head is determined by two factors, one being the magnetic torque of the clutch assembly, which is a constant, and the second being the inertia torque of the head itself. Up until now, manufacturers have had to sacrifice screwing a closure onto a container at a preferred torque value when the line speed of the containers, relative to the turret speed, varied. Now a screwcapping machine has been invented which overcomes this problem and permits the screwcapping head to be rotated at a constant speed regardless of the speed of the turret or the line speed of the containers. Also, the weight of the screwcapping head is no longer so critical. In this way, tightening torque on the cap remains constant because the two factors controlling torque remain constant. These two factors are the clutch setting and the rotational speed of the capping head.